/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.log4j.helpers;

/**
 * Utility class for transforming strings.
 * 
 * @author Ceki G&uuml;lc&uuml;
 * @author Michael A. McAngus
 */
public class Transform {

	private static final String CDATA_START = "<![CDATA[";
	private static final String CDATA_END = "]]>";
	private static final String CDATA_PSEUDO_END = "]]&gt;";
	private static final String CDATA_EMBEDED_END = CDATA_END
			+ CDATA_PSEUDO_END + CDATA_START;
	private static final int CDATA_END_LEN = CDATA_END.length();

/**
   * This method takes a string which may contain HTML tags (ie,
   * &lt;b&gt;, &lt;table&gt;, etc) and replaces any
   * '<',  '>' , '&' or '"'
   * characters with respective predefined entity references.
   *
   * @param input The text to be converted.
   * @return The input string with the special characters replaced.
   * */
	static public String escapeTags(final String input) {
		// Check if the string is null, zero length or devoid of special
		// characters
		// if so, return what was sent in.

		if (input == null
				|| input.length() == 0
				|| (input.indexOf('"') == -1 && input.indexOf('&') == -1
						&& input.indexOf('<') == -1 && input.indexOf('>') == -1)) {
			return input;
		}

		// Use a StringBuffer in lieu of String concatenation -- it is
		// much more efficient this way.

		StringBuffer buf = new StringBuffer(input.length() + 6);
		char ch = ' ';

		int len = input.length();
		for (int i = 0; i < len; i++) {
			ch = input.charAt(i);
			if (ch > '>') {
				buf.append(ch);
			} else if (ch == '<') {
				buf.append("&lt;");
			} else if (ch == '>') {
				buf.append("&gt;");
			} else if (ch == '&') {
				buf.append("&amp;");
			} else if (ch == '"') {
				buf.append("&quot;");
			} else {
				buf.append(ch);
			}
		}
		return buf.toString();
	}

	/**
	 * Ensures that embeded CDEnd strings (]]>) are handled properly within
	 * message, NDC and throwable tag text.
	 * 
	 * @param buf
	 *            StringBuffer holding the XML data to this point. The initial
	 *            CDStart (<![CDATA[) and final CDEnd (]]>) of the CDATA section
	 *            are the responsibility of the calling method.
	 * @param str
	 *            The String that is inserted into an existing CDATA Section
	 *            within buf.
	 * */
	static public void appendEscapingCDATA(final StringBuffer buf,
			final String str) {
		if (str != null) {
			int end = str.indexOf(CDATA_END);
			if (end < 0) {
				buf.append(str);
			} else {
				int start = 0;
				while (end > -1) {
					buf.append(str.substring(start, end));
					buf.append(CDATA_EMBEDED_END);
					start = end + CDATA_END_LEN;
					if (start < str.length()) {
						end = str.indexOf(CDATA_END, start);
					} else {
						return;
					}
				}
				buf.append(str.substring(start));
			}
		}
	}
}
